This invention relates to dielectrophoresis.
Dielectrophoresis (“DEP”) refers to the force experienced by particles suspended in a fluid medium when exposed to an applied electric field gradient. Due to the applied electric field gradient, differences in dielectric polarization between the particles and the fluid medium cause the particles to experience the dielectrophoretic force. This effect can be quantified in terms of the electromagnetic momentum balance via the Maxwell stress tensor, or in terms of the magnitude and distribution of the charges induced on and within the particle by the applied field. Particles, such as blood cells, experiencing strong DEP motion will typically experience a DEP force of about 10−11 N, which is about 40 times greater than a gravitational settling force and about 2×105 times larger than a maximum Brownian diffusion force.
A particle's structural and physico-chemical properties can contribute towards its DEP response. This response can also depend on the frequency of the applied electric field. Due to these dependencies, variations in applied field frequencies and external environmental conditions can simultaneously probe different particle substructures and processes. For example, some fundamental electrical properties of cells, such as membrane capacitance, membrane resistance and cytoplasmic conductance, affect their DEP response. These properties also reflect a cell's ability to maintain ion balances and are a measure of metabolic work and biological organization. Thus, DEP can provide a non-invasive method for determining the electrical properties of cell populations, down to the single cell level.